CdS:Cu nanocrystalline films were prepared by chemical bath on glass substrates at a deposition temperature of 80°C. Different Cu-doping levels were obtained by changing the volume of the Cu-reagent-solution into the CdS growing solution. X-ray diffraction ͑XRD͒ and optical absorption ͑OA͒ measurements were carried out to characterize the material. From the XRD patterns it is concluded that grains in undoped films grow in the wurtzite hexagonal phase, and in Cu-doped films they grow in the zinc blende cubic phase. The average grain size, located in the range 14-23 nm, was calculated by employing Scherrer's formula. From OA spectra the forbidden energy bandgap ͑E g ͒ was determined by using the ͑␣h͒ 2 ϰ ͑E g -h͒ relation, where ␣ is the OA-coefficient and h the photon energy. Due to the doping, E g shifts to lower values depending on the impurity level of the film. Furthermore, the dependence of E g with radius size and interplanar distances of the lattice is discussed. Gibbs free energy calculation for the Cu doping CdS process is also included.
In this work, we have obtained colloidal solutions of Si nanocrystals (Si-ncs), starting from free-standing porous silicon (PSi) layers. PSi layers were synthesized using a two-electrode Teflon electrochemical cell; the etching solution contained hydrogen peroxide 30%, hydrofluoric acid 40% (HF), and methanol. The anodizing current density was varied to 250 mA cm-2, 1 A cm-2, and 1.2 A cm-2. Thus obtained, PSi was mechanically pulverized in a mortar agate; then, the PSi powders were poured into different solutions to get the final Si-ncs colloidal solutions. The different optical, morphological, and structural characteristics of the colloidal solutions with Si-ncs were measured and studied. These Si-ncs colloidal solutions, measured by photoluminescence (PL), revealed efficient blue-green or violet emission intensities. The results of X-ray diffraction (XRD) indicate that the colloidal solutions are mainly composed of silicon nanocrystallites. The result of UV–vis transmittance indicates that the optical bandgap energies of the colloidal solutions varied from 2.3 to 3.5 eV for colloids prepared in methanol, ethanol, and acetone. The transmission electron microscopy (TEM) images showed the size of the nanocrystals in the colloidal solutions. Fourier transform infrared spectroscopy (FTIR) spectra showed different types of chemical bonds such as Si-O-Si, Si-CH2, and SiH
x
, as well as some kind of defects.PACS61.46Df.-a; 61.43.Gt; 61.05.cp; 78.55.-m; 81.15.Gh
Hydroxyapatite (HAp) and hydroxyapatite/multi-walled carbon nanotube (MWCNT) composites were obtained by the co-precipitation method, followed by ultrasound-assisted and microwave radiation and thermal treatment at 250 °C. X-ray diffraction (XRD) confirmed the presence of a hexagonal phase in all the samples, while Fourier-transform infrared (FTIR) spectroscopy elucidated the interaction between HAp and MWCNTs. The photoluminescent technique revealed that HAp and the composite with non-functionalized MWCNTs present a blue luminescence, while the composite with functionalized MWCNTs, under UV-vis radiation shows an intense white emission. These findings allowed presentation of a proposal for the use of HAp and HAp with functionalized MWCNTs as potential materials for optoelectronic and medical applications.
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